342 MARINE INVERTEBRATES 
Having examined the animal which inhabits the shell and 
gained an idea of its anatomy, we may now turn to an inspection 
of the house which it has built for itself, and here we shall find a 
delightful subject for study. 
THE GASTEROPOD SHELL 
An industrious hour of collecting upon almost any beach will 
provide the student with an abundance of interesting shells. 
Sines Putting aside the bivalves, the uni- 
valve or gasteropod shells remain- 
ing should be closely examined for 
_the purpose of becoming acquainted 
with their various conchological 
features. The collector will see 
at once that he has a number of 
species that differ more or less 
. widely in their general form, size, 
texture, and sculpture. Some 
shells will be long in proportion to 
their width, with many turns of the 
spire which probably terminates 
in a sharply pointed apex; others 
will be almost round, with com- 
Tam. 
Parts of a gasteropod shell: a, anterior 7 } 1 
canal; b, body-whorl; ¢c, columella; U, outer paratively few spiral turns which 
lip; m, mouth or aperture; p, posterior end in a blunt apex, giving to the 
canal; s, sutures; sp, spire; w, umbilicus. 
specimen outlines suggestive of a 
dome. <A wide range of characters will be found in the mouths 
or apertures of the shells, some being almost if not quite round, 
others oblong and with a notch cut into the lower portion of the 
opening, and others possibly with this notch extended into a sort 
of semi-inclosed channel. A first lesson in classification of the 
Mollusca may be taken by dividing the results of the first day’s 
collecting of univalve shells into groups according to these promi- 
_ nent shell-characters. 
A good knowledge of the parts of a gasteropod shell is essential 
to the student, and it can readily be acquired. Four specimens are 
given in the accompanying figures, representing highly divergent 
